Protein/peptide-based drugs are typically susceptible to degradation in the gastrointestinal tract and/or are not efficiently absorbed into the bloodstream from the small intestine in bioactive form. Orally delivered formulations for protein-based drugs such as insulin are being developed (Ziv et al 1994; Nissan et al 2000, Kidron et al 2004, Eldor et al 2010A, Eldor et al 2010B). One such oral insulin product is scheduled to be tested in Phase II trials and is currently being reviewed for IND status.
Trypsin inhibitors derived from soybean (Glycine max) are readily available and are considered to be safe for human consumption. They include SBTI (soybean trypsin inhibitor), which is composed of KTI (Kunitz Trypsin Inhibitor), which inhibits trypsin, and BBI (Bowman-Birk inhibitor), which inhibits trypsin and chymotrypsin. Such trypsin inhibitors are available for example from Sigma-Aldrich, St. Louis, Mo., USA. Methods for preparing BBI are described for example in U.S. Pat. No. 7,404,973.